Field of the Invention
This invention relates to an improvement in the process for recovery of metals from aqueous ammoniacal solutions wherein the metal values in the aqueous ammoniacal solution is extracted by contact with a water insoluble extractant solution in a water immiscible hydrocarbon solvent and subsequently stripped with an aqueous acid solution to strip the extracted metal values from the water immiscible organic hydrocarbon phase, the improvement wherein the extractant organic phase contains an ammonia antagonist which is a hydrogen bond acceptor, as distinguished from a hydrogen bond donor. The use of these ammonia antagonists, with either phenolic ketoxime or aldoxime extractants results in a significant reduction in chemically loaded ammonia from the aqueous ammoniacal solution containing the metal values.
In the typical extraction process of a metal from an aqueous solution containing the metal values, the aqueous solution containing the metal values is contacted by a solution of a water insoluble extractant capable of extracting the desired metal, in a water immiscible hydrocarbon solvent. After contact for a sufficient time to extract at least a portion of the metal values, the hydrocarbon solvent phase, now loaded or containing the extracted metal values, is separated from the aqueous solution phase from which the metal values have been extracted, due to the immiscibility of the organic and aqueous phases. The loaded organic phase is then typically contacted with an aqueous stripping solution thereby forming two phases again, (a) an aqueous strip phase, now containing metal values stripped from the organic extractant phase, and (b) an organic phase from which the metal values have been stripped. Again the organic and aqueous phases are separated due to immiscibility of the phases. The metal is then recovered from the metal loaded aqueous strip phase, by conventional means, such as electrowinning, precipitation or other means suitable to the particular metal, generally electrowinning being the preferred recovery means.
Both acid and ammoniacal aqueous solutions have been employed as stripping solutions in the past, one commercial process in the recovery of nickel employing an ammoniacal aqueous stripping solution.
The organic extractant currently employed commercially in extraction of metals such as copper, nickel and zinc are the phenolic oxime extractants. In the process, particularly with aldoxime extractants, it is often desirable to include in the organic extractant phase an equilibrium modifier, to provide for the most efficient extraction and "net transfer" of the metal being recovered. In the process there is a transfer of metal in the extraction stage from the aqueous feed solution to the organic extractant phase, followed by a second metals transfer from the organic phase to the aqueous strip solution phase, the two metal transfers representing the "net metal transfer" of the process. Effectively "net transfer" can be determined by observing the difference between the extraction isotherms and the strip points.
Typically equilibrium modifiers employed with the phenolic oxime extractants in the process have generally been various alcohols and esters.